At present, almost all thin-film transistors adopt a planar channel structure, that is, the channel is flat. With a continuous decrease of a length of the channel, a gate control loss caused by a short channel effect and a soft saturation phenomenon of an output current are more and more severe, and have become one of the major challenges for a small-size thin-film transistor. Some researchers have attempted to solve this problem by adopting a vertical channel structure, but the thin-film transistor with the vertical structure faces many new problems in aspects of process and integration. In addition, in the field of photoelectric detection, a thickness of the channel directly determines light absorption efficiency. However, if the channel adopts the same thickness, an increase of the thickness will increase a contact resistance of a source-drain electrode region, which is not conducive to a fast switching of the thin-film transistor.